How much AC is usually let through a MUR860 rectifier bridge? - diyAudio
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Old 5th April 2005, 08:14 PM   #1
bg4533 is offline bg4533  United States
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Default How much AC is usually let through a MUR860 rectifier bridge?

How much AC voltage is usually let through a MUR860 rectifier bridge? Is it dependent on AC voltage?
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Old 5th April 2005, 09:43 PM   #2
Eva is offline Eva  Spain
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I think you've accidentally mistaken current and voltage somewhere in your sentence

Remember that MUR860 is rated at 600V DC peak and 8A average current

Peak current may greatly exceed rated average current as long as a small enough duty cycle is employed. However, rated peak voltage must not be exceeded
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Old 5th April 2005, 09:54 PM   #3
bg4533 is offline bg4533  United States
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I am somewhat of a beginner so I don't really know what I am talking about.

What I am trying to ask reworded:
What would be a normal measurement of AC voltage on the DC side of a MUR860 rectifier bridge?

-----
In response to your question and a bit more thinking:
Is AC current on the DC side a bigger problem? What would be a normal measurement for this?
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Old 5th April 2005, 10:45 PM   #4
BWRX is offline BWRX  United States
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it depends on the voltage rating of the transformer secondary it is hooked up to and also the current draw of the load.
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Old 5th April 2005, 11:01 PM   #5
bg4533 is offline bg4533  United States
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I am away right now and I can't recall the exact measurements.

I am trying to replace the bridge in my DAC-AH.

The transformer has 2 taps rated at 18V each (center tapped I think). Each tap is hooked up to one side of the bridge. The DC output I got seemed reasonable. With no load I measured around .5V of AC on the DC side. I really don't know, but that seems pretty high to me.
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Old 5th April 2005, 11:13 PM   #6
BWRX is offline BWRX  United States
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do you mean the transformer has two secondary windings and they're wired to provide a positive voltage rail, negative voltage rail, and common ground using one bridge rectifier like in this picture:
Click the image to open in full size.

or by two taps do you mean just two wires connected to a bridge rectifier like in this picture:
Click the image to open in full size.

the voltage rating of the transformer secondary is in VAC RMS. if you are using either configuration the DC voltage at the filter cap terminals should be approximately:
VDC = VAC * sqrt(2) - 1.4

the 1.4 comes from the 0.7V drops (approximately) across the rectifier diodes.

if there is no filter cap and you're just measuring the DC voltage at the bridge rectifier terminals with an RMS multimeter than it will be a little higher than the voltage rating of the transformer secondary.
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Old 5th April 2005, 11:30 PM   #7
bg4533 is offline bg4533  United States
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The top diagram is what I am dealing with. Positive, negative and ground.

I know how to calculate what the DC voltage should be. The DC voltage I got was basically what I expected. (I estimated in my head, did not calculate)

I measured AC voltage on the DC side of the rectifier. My thought was that I should measure little to no AC voltage. ~I measured 0.5V
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Old 5th April 2005, 11:34 PM   #8
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If you're measuring with no caps, you get pulsed DC, and most DMMs can't measure this accurately. Stick 6800uf or so of capacitance on each rail then try again.
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Old 5th April 2005, 11:52 PM   #9
bg4533 is offline bg4533  United States
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Quote:
Originally posted by pinkmouse
If you're measuring with no caps, you get pulsed DC, and most DMMs can't measure this accurately. Stick 6800uf or so of capacitance on each rail then try again.
Hmmm...that is probably the case then. My soldering station died Sunday. A new one is on the way. When it arrives I will test things out and if there is a problem I will report back.

Thanks for the help everyone.
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Old 12th April 2005, 03:10 AM   #10
bg4533 is offline bg4533  United States
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I just recieved a scope, but I still don't really know how to use it.

When I look at the negative rail of the PSU things are smooth as expected.

When I look at the positive rail things dont looks so good. After a 7812 regulator I get what looks like the top half of a sawtooth. Before the regulator and after the rectifier I get something similar except the lines are blurrier and there are horizontal disconuities between the wave. It is the same before and after the filter caps.

Is this how this is supposed to be or did I screw something up?
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